Photoproduction of $J/\psi$ in association with a $c\bar{c}$ pair

TL;DR

This paper analyzes the production of $J/$ mesons with a charm-anticharm pair in photon collisions, comparing theoretical predictions with experimental data and exploring the role of different production mechanisms.

Contribution

It provides analytical calculations of subprocess amplitudes within the color-singlet model for $J/$ photoproduction with a $cc$ pair, including predictions for collider experiments.

Findings

At LEPII, the processes do not fully explain experimental data, suggesting the need for color-octet mechanisms.

Resolved photon channels dominate at photon colliders in certain $p_t$ regions.

The process offers a new way to test color-singlet contributions in $J/$ production.

Abstract

Based on the color-singlet model, we investigate the photoproduction of $J/\psi$ associated with a $c \bar{c}$ pair with all subprocesses including the direct, single-resolved, and double-resolved channels. The amplitude squared of these subprocesses are obtained analytically. By choosing corresponding parameters, we give theoretical predictions for the $J/\psi$ transverse momentum distributions both at the LEPII and at the future photon colliders for these subprocesses. The numerical results show that at the LEPII these processes can not give enough contributions to account for the experimental data, and it indicates that the color-octet mechanism may still be needed. At the photon collider with the laser back scattering photons, the resolved photon channe will dominate over the direct one in small and moderate $p_t$ regions with large $\sqrt{s}$. By measuring the $J/\psi$ production associated with a $c\bar{c}$ pair, this process can be separated from the inclusive $J/\psi$ production and may provide a new chance to test the color-singlet contributions.